Computerized tomography by definition provides two dimensional (2D) images of planes (planar views) in a patient's body. Often times it is important for the viewer (diagnostician and/or doctor) to be able to obtain three-dimensional views rather than planar views of the interior of the patient's body. For example, in surgical procedures it is extremely helpful if the doctor can see a three-dimensional view of the interior of the body in the area of the operation. Prior to brain surgery which are supplemented by three-dimensional views elaborate measuring methods are used to increase the probability of a successful operation.
At present time the three-dimensional views are obtained either by special x-ray equipment such as for example disclosed in the U.S. Pat. No. 4,309,615 or by taking a sequence of tomographic views of the portion of the body of interest and subsequently processing these views to provide the desired three-dimensional view. See the article entitled "Display of 3D Information in Discrete 3D Scenes Produced by Computerized Tomography" by J. K. Udupa, published in The Proceedings of the IEEE, Vol. 71, No. 3, Mar. 83, pp 420-431 (including an extensive bibliography).
In the prior art, to acquire and display a 3D image of an organ using the regular 2D tomographic equipment, it is necessary to acquire a series of parallel slices to obtain surface values necessary to construct a 3D image. Thus, in the prior art a great many planar slices are acquired, the values of the pixels in the slices are used to find surface pixel values between the slices. The surface pixel values are used to project the 3D image.
In the latter example, there is a need to reduce the number of views in order to maximize throughout and to prevent the unnecessary exposure of the patient to radiation. As a result the number of views acquired are minimized and consequently the description of the shape of the organ of interest is not complete. Accordingly, there is a need to interpolate to obtain the organ's shape from the acquired partial data of the spaced apart planar views. The interpolation should ideally reconstruct the actual shape of the organ and practically reconstruct the actual shape with minimum deviations.
Since the shapes of internal body organs are highly irregular, with no simple mathematical description, prior known methods all have serious limitations such as a lack of fidelity and unnecessary artifacts.
Thus, it is the object of this invention to provide a reliable method of obtaining a full description of the shape of internal organs from a series of planar slices of those organs. The result of applying the process described is a three dimensional binary bit matrix, in which the regions of bits having "1" values correspond to regions of space occupied by the organs of interest, while regions of bits having "0" values correspond to unoccupied space. This 3-D matrix can then be used to present the structure of the organs to the interested viewer in forms, such as a shaded surface image, well known to those skilled in the art.
In addition to the need for an ambulance of views, a prior art problem is to locate the edge of the organ of interest. In general, thresholding is practiced to convert the originally acquired data into binary maps to determine the edges of the organs. Interpolation is then done between portions of the edges having opposite bit values. However, the functional values (not the binary values) of the given plane image are used for the interpolation between the planes. The interpolation acquired values are converted to binary maps using thresholding. Accordingly a prior art problem is the necessity of using threshold discriminators to convert the interpolated functional values to bit values. The prior art is also plagued with a "staircase" artifact in the images of the surface of the organ of interest.